Classification of Southern California
Chitons

Phylum Mollusca

Class Polyplacophora

Order Neoloricata

Members of the Phylum Mollusca contain a variety of common
characteristics. Some common characteristics include a soft body
surrounded by some sort of an outer shell secreted by the mantle. The
shell may be external or internal or secondarily lost. A strong
muscular foot used for locomotion is another common characteristic of
the Phylum Mollusca. The molluscs are extremely large in species
numbers, approximately 300-400 species of molluscs occur in the
intertidal zone of Southern California. The Chitons belong to the
Class Polyplacophora, whose members can distinguished by eight
calcareous plates which are embedded on a muscular girdle. Several
gills are located on either side of the foot which serve for
respiration. The girdle may contain scales, hairs or granules on its
surface. Chitons are herbivores, feeding mostly on algae. Chiton
fossils date back as far as half a billion years ago, with a increase
in diversity since then. The Order Neoloricata

Family Ischnochitonidae

Genus Lepidochitona

Species hartwegii

Family Callistoplacidae

Genus Nutallina

Species fluxa

Family Mopalidae

Genus Mopalia

Species Muscosa

The chitons can be divided into three Families, the
Ischnochitonidae, Callistoplacidae and the Mopalidae. The Family
Ischnochitonidae contains the Lepidochitona hartwegii and can
be distinguished from other families from its scaley girdle and a
variety of valve patterns. Members of the Genus Lepidochitona
are characterized by a flat, depressed tail valve. The Family
Callistoplacidae can be distinguished by spines or spicules on the
girdle and once again the valves can have a variety of patterns. The
members of the Genus Nutallina can be separated from other
genera by 9 to 12 slits in the head valve and long, smooth insertion
plates. The Family Mopalidae can be separated from other families by
long hairs or spicules on the girdle. The Genus Mopalia has a
notched tail valve with a single pair of slits on either side.

Natural History of Southern California
Chitons

General:

Chitons occupy a great range from high in the intertidal zone to
depths of over 12,000 feet, and from the tropics to the polar seas.
They become most abundant on temperate rocky shores because that's
where they can find a hard substratum for attachment by their
well-adapted broad foot, and it's also the place where their foods
are the most abundant. Some chiton species occupy the outer coast
because they are able to withstand the buffeting of heavy surf, but
others occupy the quieter area behind the offshore reefs or rocks, in
embayments, and in tidepools.

About 20% of all chitons can be found along the west coast from
Alaska all the way down to southern California, which is more than
any other coasts in the world. Fifty species and subspecies are found
in Monterey Bay alone. A large and diverse chiton population is also
found in New Zealand and Australia.

Chitons are generally sluggish and many are nocturnal and remain
concealed under rocks during the day, therefore their foods mainly
consist of algal films scraped off the rocks by the radula, but some
also consume animal matters. More importantly, the diets of
individuals of any one species may differ in different habitats.

Specific Species:

Lepidochitona hartwegii: it is always found associated with
Pelvetia fastigiata, which is the principle diet for the
chiton. This chiton in found in southern California in the mid-tide
zone at the rocky shores, especially at Little Corona and Palos
Verdes.

Nuttalina fluxa: The coralline algae is the principle food
for this chiton. They have sea gulls that prey on them. This species
is the most frequently encountered in southern California, and they
live in pits in the rocks in the mid- and upper-tide horizon all all
rocky shores and some of the rock jetties in southern California.
They live in depressions which are about the shape and size of the
animal, and the depressions are exposed at low tide. Often the
depressions are so deep that the back of the chiton is below the
surrounding rock, thus they have become sessile in habitat,
sacrificing grazing habitat for greater protection. The modifications
in habits and habitat assure the species to perpetuate. This species
of chiton is mainly preyed upon by western gulls. In some localities
as much as 15 percent of the chiton population are taken during
western gull's breeding season.

Mopalia muscosa: this species maintains a home where it
emerges at night to feed on the algae; it travels as far as 2 feet
from its home and it will return. They are common in southern
California marine habitats. It is found in the mid-tide zone
generally within rock crevices among barnacles, and it has also been
collected from the boat floats of the principal bays and harbors of
southern California. This species is most common on rocks and in
tidepools, middle and low intertidal zones in regions of low to
moderate surf; they have a big range from Queen Charlotte Islands
(British Columbia) to Isla Cedros (Baja California). The mossy chiton
is also one of the few west coast species that does well in
estuaries. They remain in place during the day or whenever exposed by
low tides. Individuals living permanently submerged in tidepools did
not have the same homing behavior. The chiton feed mainly on the red
algae Gigartina papillata and Endocladia muricata and
the green alga Cladophora whenever they are available, but in
other places the species appear to be unselective herbivores, and the
gut can contain animal matter for up to 15%

Distinguishing Characters of Southern
California Chitons

Lepidochitona hartwegii (Gray, 1821). Common name-Hartweg's
Chiton. Previous name- Cyanoplax hartwegii. The Hartweg's
chiton has a bright blue interior of valves and an oval shaped dark
green to grey body. This species often grows to a length of two
inches. The Hartweg's chiton is granulated on the surface of the
girdle and the valves often have a white streak along the posterior
end. This species is found in the mid-tidal zones on or under rocks
from Monterey, Ca to Baja California.

Nuttalina fluxa (Dall, 1871). Common name- Califronia
Chiton or Rough chiton. The California chiton can be distinguished by
its small size which is usually 1.5 inches or less in length. The
girdle is often brown to pink in color and has several spines on it.
The California chiton is found in pits in the rocks in the upper and
mid-tidal zone and on many rock jetties in Southern California. This
species of chiton is the most common in Southern California.

Mopalia muscosa (Gray, 1847). Common name- Mossy Chiton.
The mossy chiton is often much larger then the California Chiton. The
Mossy Chiton can grow to a length of 2.5 inches. The shell is often
dull gray to black and the girdle contains stiff curled hairs. The
mossy chiton is found in rock crevices in the mid tide zone and the
range is from Alaska to Baja California.

Key to Species of Southern California
Chitons

1. Shape of organism is oval, flattened; color is grayish green;
tail valve is depressed; found on or under rocks or under algae
intertidally...................Lepidochitona hartwegii

2. Nine to twelve slits in the head valve; long smooth insertion
plates; found on rocks in the intertidal
zone............................Nuttallina fluxa

3. Shape of organism is oval, flat; color varies from dull brown
to dark olive or gray; the stiff mossy tails on the girdle is a
common feature; tail valve notched behind, with a pair of slits at
sides; found on rocks in intertidal zone protected from heavy wave
action or in tide pools...............................Mopalia
muscosa